Python 3.7 + Numpy + pandas数组在范围内选择数据

Question

Ok I'm going to try to explain my problem, I have a csv file with data, the data is wavelength and amplitude, the image is include here.

CSV data

So, I want to select only data between 500nm and 800nm (wave),

import pandas as pd
import numpy as np
excelfile=pd.read_csv('Files/660nm.csv');
excelfile.head();
wave = excelfile['Longitud'];
wave = np.array(wave);
X = excelfile['Amplitud'];
X = np.array(X);
wave = wave[(wave > 500) & (wave < 800)]

This does what I want in first instance, but I want to extend this selection to the column of amplitude (X), to have two arrays of the same dimensions. In my actual code I have to make an index to select the data in the amplitude array(X):

indices = np.arange(382,775,1)
X = np.take(X, indices)

But this is not the best practice, if I cant extend the first column selection to the the amplitude column I don't have to make another array to index the X array, and check the extension of the array, any idea about it ? Thanks.

Answer 1

Like @ALollz pointed out, you shouldn't split the DataFrame up. Instead just filter the whole dataframe on wavelength. See the docs for DataFrame.loc

import pandas as pd
import numpy as np

# some dummy data
excelfile = pd.DataFrame({'Longitud': np.random.random(100) * 1000,
                          'Amplitud': np.arange(100)})

wave = excelfile['Longitud']
excelfile_filtered = excelfile.loc[(wave > 500) & (wave < 800)]
X = excelfile_filtered ['Amplitud'].values  # yields an array